This invention relates generally to methods and systems for detecting low paper in a printer and, more particularly, to methods and systems for detecting multiple levels of paper supply in a printer.
Printers are used for depositing indicia on paper to produce documents and the like. The paper on which the indicia are deposited or printed may be provided to the printer in separate sheets or in continuous form such as a roll or fan-folded sheets. The paper on which the indicia are printed is typically provided in a supply unit such as a well, cassette, recess, or the like as is well known. To prevent the operation of the printer when no paper is available for receiving the indicia, detectors were developed that sensed the absence of available paper in a supply unit and provided an indicator of the paper unavailable condition so an operator could replenish the supply. Because the condition of the paper supply is sensed prior to the printing mechanism for depositing the indicia, the paper unavailable condition could occur during the printing of a multiple page document. Also, printing of a document on a roll of paper might also commence before detection of the end of the paper roll by the supply detector. To prevent the likelihood that a paper supply would be exhausted during a printing operation, low paper condition detectors were developed.
Low paper condition detectors monitor the paper supply unit and determine when the paper supply has reached a predetermined threshold and signals a low paper condition without terminating an ongoing printing operation. At the conclusion of the ongoing printing operation, if it finishes before the supply is exhausted, the operator may then replenish the paper supply to prevent the subsequent interruption of a later printing operation for the lack of paper. Thus, low paper condition detectors facilitate the scheduling of paper supply replenishment at a time that is not likely to interfere with an ongoing printing operation. To further facilitate paper supply replenishment scheduling or to assist an operator in determining whether sufficient paper is available for the printing of a multiple page document or a long document, detectors for providing multiple indications of the paper supply level were developed. These detectors typically include multiple sensors that detect the presence or absence of paper in the vicinity of a sensor. When the multiple sensors are arranged along the depth of a stack of paper sheets in a supply or along the radius of a paper roll supply, the two adjacent sensors that detect opposite conditions provide an indication of the paper supply condition. That is, a sensor indicating no paper is present and an adjacent sensor that indicates paper is present demarcates an approximate boundary of the paper supply. For example, four sensors equally spaced in longitudinal array along the depth of a paper supply or the radius of a paper roil may have second and third sensors indicating opposite conditions. From the signals from the sensors, a controller or processor may determine that the paper supply is between 50% and 75% full. When all four of the sensors indicate the presence of paper, the supply is full, while all four sensors indicating the absence of paper indicates the supply is below the last sensor in the array. This last condition is typically used to signal a low paper condition and the other possible signals from the detector are used to determine the approximate level of the paper supply for determining whether substantial printing operations may be performed without exhausting the available paper supply.
While the detectors that provide multiple indications of the status of a paper supply are useful, they do not provide a continuous indication of the level of the paper supply available. To address this deficiency, a low-paper sensing device was disclosed in U.S. Pat. No. 5,960,230 to Peter. The device of that paper uses a sensor of the type described above to indicate more than one level of paper supply and supplements this paper level indication by counting the number of sheets of paper delivered to a printer from the supply between detection of level indications. This data may then be used to count down to an empty condition or to calculate an approximate number of sheets left in the supply. Thus, this device requires the addition of a counting mechanism to the printer paper supply unit to more accurate assess the status of the printer paper supply between level indications.
One limitation of the above-described device is the requirement for a sheet counter. In printers that use paper sheets, additional counter circuitry and software for adjusting the sheet count through averaging and the like to compensate for some measurement errors is required. For printers that use paper roll supplies, the counter does not successfully indicate the amount of paper remaining because it is not provided in a sheet by sheet manner.
Consequently, what is needed is a way of continuously indicating the status of the paper supply.
What is need is a way of refining measurements of available paper for printing without requiring the counting of sheets.
The above-noted limitations of previously known systems and methods for indicating the level of available paper in a paper supply for a printer have been overcome by a system and method that operate in accordance with the with principles of the present invention. The system of the present invention comprises a signal emitter for emitting a signal into a paper supply and a variably activated receiver for generating a paper supply level signal, the variably activated receiver is mounted at a location for selectively receiving the emitted signal from the signal emitter in relation to the level of paper in the supply. The signal emitter may be an infrared (IR) or electrical source. The variably activated receiver is preferably a photoresistor having a resistor value that changes in accordance with the amount of infrared radiation received at the surface of the photoresistor. The photoresistor is coupled to a signal circuit that generates a continuously variable signal across a range and the signal variation follows the resistance value of the photoresistor. The variably activated receiver has sufficient length such that only a portion of the receiver is exposed to the signal emitter as the paper supply between the emitter and receiver diminishes. When the length of the receiver is fully exposed to the signal emitter, the receiver generates a saturation signal that defines one end of the range of the signal generated by the receiver.
In an alternative embodiment of the present invention, a light guide is interposed between the variably activated receiver and the signal emitter. The light guide collects the infrared signal emitted by an optical signal emitter and transmits the light to a variably activated sensor. As a longer section of light guide is exposed to the optical signal emitter, more light is delivered to the surface of the variably activated receiver. The intensity of the delivered light causes a parameter of the receiver to vary and generate a continuously variable signal indicating the relationship between the signal emitter, light guide, and paper in the paper supply.
The method of the present invention includes emitting a signal into a paper supply and generating a continuously variable signal indicative of the amount of emitted signal being received by a variably activated receiver coupled to a paper supply. Preferably, the emitted signal is an infrared signal and the continuously variable signal is indicative of the amount of light incident upon the variably activated receiver. The method of the present invention may also include coupling the emitted signal through a light guide to the variably activated receiver. A length of light guide, a continuous light source, or array of discrete light sources may be provided along the length of the paper to continuously provide an amount of light indicative of the amount of available paper in a paper supply.
Because the system and method of the present invention may be used to generate a continuously variable signal indicative of the paper supply level, a user may specific a low paper condition level anywhere along the range of the supply capacity. Thus, the low paper condition detector need not be physically arranged to correspond to the desired level for generation of a low paper condition signal. Instead, a user may enter the low paper condition through a software interface and the control program for the printer may store the low paper condition parameter for comparison with the signal indicative of the paper supply level. Additionally, with data regarding the length of a standard roll or thickness of a sheet, the system and method of the present invention may be used to compute a remaining number of sheets or roll length for display to an operator. In this manner, a continuous indication of the paper supply is provided for operator control of the printer and printer supply replenishment.
It is an object of the present invention to provide a continuously variable signal indicative of paper supply level in a printer.
It is an object of the present invention to support user definition of the low paper condition level without requiring mechanical adjustment of the paper supply sensors.
It is an object of the present invention to provide continuously variable indicator of the remaining paper supply in a printer.
These and other advantages and features of the present invention may be discerned from reviewing the accompanying drawings and the detailed description of the invention.